As a transparent electroconductive layer included in a transparent electroconductive film used as a material of a touch panel or display, or used in a solar cell or the like, indium tin oxide (ITO), tin oxide, zinc oxide, or the like is widely used. It is known that such a transparent electroconductive layer is formed by, for example, a physical vapor deposition method (PVD method) such as a magnetron sputtering method or a molecular beam epitaxy method; a chemical vapor deposition method (CVD method) such as thermal CVD or plasma CVD; or an electroless method. Regarding the transparent electroconductive layer used in such a transparent electroconductive film, it is necessary to ensure sufficient transparency, and it is also necessary that variations in characteristics such as the surface resistivity and optical properties be small. Indium tin oxide (ITO) is a material that is excellent in the above characteristics and is widely used as a transparent electroconductive layer currently. However, indium used as a raw material may be exhausted and thus searching for an alternative material to ITO has become an urgent task in terms of resources and the cost. Zinc oxide is an abundant material in terms of resources and has attracted a great deal of attention as an alternative material to ITO. However, a transparent electroconductive layer composed of zinc oxide generally has a property that the surface resistivity increases when the transparent electroconductive layer is left to stand in air in the form of a thin film. Accordingly, in order to use zinc oxide as a transparent electroconductive layer, it is necessary to take measures, for example, to excessively increase the thickness of the layer. As a measure to counter an increase in the surface resistivity, Patent Document 1 describes that an aqueous solution containing a trivalent metal cation is used as a modifying agent for a zinc oxide film to decrease the rate of variation in the surface resistivity to 1.2 times or less.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-39712